1. Field of the Invention
This invention relates to improvements in a swivel joint, and more particularly to an improved swivel joint especially adapted for supporting a lamp in an angularly adjusted position about two transverse axes.
2. Brief Description of the Prior Art
The heretofore conventional swivel joints were of relatively complicated structure having a multiplicity of parts, which results in an expensive mechanism. Despite the complexity of the mechanism, the rotatively mounted stem to which the lamp reflector was attached was relatively difficult to rotate, in some instances, to angularly adjust positions, or conversely, if easy to rotate, it was difficult to clamp securely after adjustment.
Moreover, in some prior art joint constructions, the rotatively mounted stem could move longitudinally and axially in its mounting, and consequently, would be disturbed in its exact relationship with the coacting transverse second axis.
In the prior art an exact weight balance and balancing of the bracing springs is required for the joints to maintain the structure in any one of a plurality of possible positions. Frequently, however, less than a perfect interaction of parts is achieved and the device will not hold several desired positions. In the higher priced versions of the prior art devices, the balancing between the weight of the arms and shade are correctly matched with the spring system, however, if any change is made, i.e. a larger bulb or different shade, the balance is thrown off and the unit will not function as intended. In the lower priced units, because of the inbalance between the arms, shade and springs, the unit is basically non-functional as intended. In both units, the higher and lower priced, the aesthetics cannot be improved because of the need for the balancing springs. The prior art units are unattractive as well as generally unfunctional.
The swivel joint as disclosed in U.S. Pat. No. 3,480,304 by Mehr, is of a relatively uncomplicated nature and exists of fewer parts than the prior devices. It does, however, have inheritant problems which, up until the instant invention, have not been overcome. A major problem with the prior art is that adjustments as to the angle of the arms of the lamp is made by loosening a screw device, placing the arms in the desired position and then tightening the screw or knob until the pressure clamps the arms tightly and holds them in the desired position. This technique is illustrated in FIG. 4 of the above patent wherein a pin 31, having a head 32 at one end and a threaded opposite shank end 33, extends transversely through the brackets 27 and 28 and through the body sections 24 and 25 and then engages the bracket 27. An adjusting knob 34 is attached to the threaded pin end 33 and it is through the tightening of this adjusting knob 34 that the arms of the lamp are held in the desired position. The adjusting knobs or screws in this type of device require few turns of the threaded section to tighten them to a clamping position, and conversely very few turns, or a small amount of slippage releases the tension created and allows the arms to slip. This problem becomes more apparent as time progresses and the unit is used more.
The parts of the units described above are generally made from plastic, except for the threaded pin or screw, to allow the unit to be made more economically as well as lighter. The plastic sections through which the threaded piece pass, have a tendency to wear and enlarge the hole, requiring more and more tension to be placed to hold the arms in position until eventually the units are so worn they can no longer be forced into the stationary position. The lamp unit is then no longer useable in its original form and must be secured by other means.